Transcutaneous prosthesis

ABSTRACT

A transcutaneous prosthesis which includes a first component shaped for implantation into a bone, a second component intended for location between the bone and the skin, the second component having a surface treatment for stimulation of fibroblastic cell proliferation and attachment of epithelial cells, and a third component intended for location exterior to the skin surface having a low surface energy which deters bacterial adhesion.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.11/306,584, filed on Jan. 3, 2006, which is a continuation of U.S.application Ser. No. 10/311,589, filed on Apr. 28, 2003, now U.S. Pat.No. 7,014,661, which is a national stage filing of PCT/GB01/02771, filedon Jun. 22, 2001, which claims the priority of GB 0015479.9, which wasfiled on Jun. 23, 2000.

FIELD OF THE INVENTION

This invention relates to transcutaneous prosthesis and includes amethod of fitting a prosthesis having a transcutaneous component to apatient.

BACKGROUND OF THE DISCLOSURE

Amputation of limbs or digits can occur due to trauma or because ofsurgical removal. Examples of trauma include loss of fingers inmachinery accidents, loss of limbs in car accidents or as a result ofland mine explosions. Surgical removal can also be indicated as a resultof cardio-vascular disease, diabetes and cancerous tumours to the boneor soft tissues.

After amputation, it is common to fit an external endo-prosthetic devicethat is attached to the body via by a skin interface. This commonlyinvolves the manufacture of a custom-made socket which is secured to thestump using straps or clamps. A number of disadvantages arise from theuse of such endo-prosthetic devices. For example:

(1) Skin is not a satisfactory high load bearing structure and oftenbreaks down under load, becoming inflamed and uncomfortable and, insevere cases, pressure sores are formed which are difficult to heal.

(2) Changes in the shape of the stump may mean that a new custom-madesocket is required.

(3) The use of sockets for receiving the stump are commonly sweaty anduncomfortable.

(4) Where a joint is involved, the external prosthesis is usually movedby muscle groups situated at a distance from the attached prosthesis andtherefore motion is inefficient and unnatural.

OBJECTS AND SUMMARY

A major object of the present invention is to provide a prosthesis whichovercomes some or all of the above disadvantages.

According to one aspect of the present invention there is provided atranscutaneous prosthesis which comprises a first component shaped forimplantation into a bone, a second component intended for locationbetween the bone and the skin, the second component having a surfacetreatment for stimulation of fibroblastic cell proliferation andattachment of epithelial cells and a third component intended forlocation exterior to the skin surface having a low surface energy whichdeters bacterial adhesion.

The prosthesis provided by the present invention is thus anintra-osseous transcutaneous prosthesis (ITAP) and has a number ofadvantages. For example, the first component is attached directly toload-bearing parts of the bony skeleton such that load is transmittedthrough bone. This means that the patient is able to apply much morepower to the prosthesis. Also, motion and perception of movement is morenatural because of the bone attachment. Moreover, because the skin takesno part in transmitting the load from the bone to the external part ofthe prosthesis, there is no pressure on the skin surface which wouldcause inflammation or discomfort.

The first component is formed with some suitable means for preventingrotation of the component in the bone which may comprise flutes orgrooves or functionally similar shaped surfaces. These surfaces may beshaped to fit the profile of the intramedullary cavity, where present.Also, the first component is preferably provided with a surfacetreatment which encourages osseous integration. Suitable surfacetreatments include hydroxyapatite which is a hydrated calcium phosphate.The surface may also be formed with small apertures or pits to encourageintegration between the bone and the first component. Where micro pitsare formed in the surface, these may be of the order of 20 to 500microns in size, preferably 20 to 100 microns.

The second component extends between the bone and the epithelialsurface. This component is provided with a surface treatment forstimulating fibrous tissue ingrowth. Again, this component may betreated with an hydroxyapatite or aluminium oxide coating and thecoating treated with materials which encourage the adhesion ofepithelial cells to the second component. This component may also have acoating which is porous to encourage soft tissue ingrowth Materialswhich encourage such growth include adhesion promoting proteins such asfibronectin or laminin. In order to aid adhesion of the fibrous tissueto the second component, the hypodermis is preferably surgically removedduring the procedure of installing the prosthesis. The goal is to attachthe skin to the implant to prevent movement of the skin and shear forcesseparating epithelial cells at the interface and underlying dermis andthereby permitting infection to enter between the skin and theprosthesis.

The third component comprises the exterior part of the prosthesis andthis has a low surface energy which deters bacterial adhesion. A lowsurface energy can be achieved by coating this part of the prosthesiswith a non-stick material such as a diamond-like carbon, a fluorinatedpolymer or a silicone polymer.

The prosthesis may be made up from separate components connectedtogether, or two or more of the components may be formed integrally andgiven appropriate surface treatments.

The external component will preferably include a safety devicecomprising a linkage which breaks under an unusual load such as, forexample, one caused by the patient falling. This will allow the externalcomponent to detach from the skeletal and transcutaneous componentwithout causing damage to the bone or to the skin. An additional featurewhich will protect the fixation of an intramedullary post is an externaldevice which limits torque transmitted to the adjustable fixation. Thetorque transmitted may be adjustable so that with time, the transmittedtorque can be increased, as the internal component integrates with thebone.

In a further preferred embodiment of the present invention the secondcomponent may be provided so as to extend outwardly from the first andthird components in a manner that increases the external surface area ofthe second component. The second component may also be provided withthrough holes which further increase the external surface area and allowgrowth of tissue through the second component. This has been found toadvantageously facitate the integration of the component with fibroustissue growth.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is illustrated by the accompanying drawings in which:

FIGS. 1 and 2 are diagrammatic views through part of a deer's antler andskull;

FIG. 3 is a diagrammatic part section showing a transcutaneousprosthesis in accordance with an embodiment of the invention, fitted toa patient.

FIG. 4 is a perspective view of a preferred embodiment of a prosthesisin accordance with the present invention drawn on a larger scalecompared with FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, the present invention was in part stimulatedby study of the skin-bone interface around red deer antlers. This is aunique structure and may be thought of as a biological model for atranscutaneous implant. The deer antler at periods of the year is veryheavily loaded during the rut. Histological examination indicates thatthe layer of skin epithelial cells become thinner as the epitheliallayer approaches the antler, such that at the antler-skin interface anepithelial skin layer is only about one cell thick The dermis isintimately attached to the bone (pedicle) interface. The attachment isachieved through a series of “Sharpeys fibres” which attach to thedermis and to the bone and prevent differential skin movement. Antlersdo not normally become infected and the bone structure is invaginatedwith small pores measuring 18 to 40 microns in diameter. This helps theinterface between the dermis and the bone to resist shear stresses.These features are shown in FIGS. 1 and 2 of the accompanying drawings.

The prosthesis of an embodiment of the present invention is shown inFIG. 3 and may be considered an artificial analogue of the deer'santler. The prosthesis comprises a first component (1) which is insertedinto the intramedullary canal of a bone (2). Component (1) is formedwith longitudinally extending cutting flutes which engage in the bone asthe prosthesis is inserted into the intramedullary canal and resistsrotation The surface of the component (1) may be coated with a materialto encourage osseous integration such as a hydroxy apatite materialand/or be micro-pitted. The second component (4) extends from the end ofthe bone to the surface of the skin. This component may be cylindricalas drawn, or could be flattened to a mushroom shape, thereby increasingthe surface area over which the soft tissue can be attached. Component(4) is given a surface treatment to encourage attachment of theepithelial to the implant. Such surface treatments include giving thesurface a micro-pitted structure and/or coating the surface withadhesion proteins such as laminin or fibronectin which encourage fibrousgrowth into the surface of the component (4) of the prosthesis.

Prior to installing the prosthesis, the hypodermis is preferablysurgically removed. Further, a surface is provided on the secondcomponent which is porous and promotes fibrous tissue ingrowth. Suitablematerials for coating the surface include alumina oxide ceramics andhydroxy apatite. This surface, preferably after being given a poroussurface treatment, is coated with an adhesion promoting protein, e.g. byspraying the prosthesis with a solution of the adhesion-promotingprotein, by dipping the prosthesis in a concentrated solution of theprotein and freeze drying, or by dipping into a sterile solution of theadhesion-promoting protein prior to implantation

The removal of the hypodermis surgically during the amputation andinstallation procedure assists in stimulating attachment of the skin tothe implant and thereby prevents shear forces on the skin separating theepithelial cells at the interface.

The third component (5) of the prosthesis extends from the skin and isgiven a non-stick surface on its exterior portion Suitable materialsinclude fluorinated polymers such as polytetrafluoroethylene,siliconised polymers and diamond like carbon. The presence of anon-stick surface discourages bacteria from attaching to the prosthesisand helps to prevent infection. The non-stick surface may be applied tothe exterior portion of the third component (5) using the technique ofchemical vapour deposition (CVD). The use of CVD is well known in theart for applying a surface of diamond-like carbon. When applying asurface layer of diamond, as disclosed in EP-B-0545 542 the methodgenerally involves providing a mixture of hydrogen or oxygen gas and asuitable gaseous carbon compound such as a hydrocarbon, applying energyto that gas to dissociate the hydrogen into atomic hydrogen or theoxygen into atomic oxygen and the carbon into active carbon ions, atomsor CH radicals and allowing such active species to deposit on thesubstrate to form diamond. The energy to cause dissociation may beprovided in a number of ways common to the art, for example by hotfilament or by microwave source. A non-stick surface of fluorinatedpolymer or silicone polymer may be applied to the third component bypolymerising a monomer or prepolymer in contact with the component.

It may be convenient to apply the low energy surface treatment to thethird component while masking the remaining components of theprosthesis. Also, the second component of the prosthesis may be treatedwith the adhesion-promoting protein after applying the low energysurface to the third component, and it may be desirable to mask thethird component while applying the adhesion-promoting protein.

The third component may be connected to an artificial limb or digit. Forexample, in the case of a replacement finger or part finger, the firstcomponent may be implanted into the remaining bone with the secondcomponent instituting the transcutaneous portion, and the thirdcomponent extending beyond the severed stump. An artificial digit orpart digit can then be attached to the third component.

The prosthesis may be implanted either in a one-stage procedure or in atwo-stage procedure where the first component is implanted into the boneand allowed to integrate before the transcutaneous part is attached.

There is shown in FIG. 4 a further preferred embodiment of the presentinvention wherein the second component (4) is extended in an outwarddirection perpendicular to the first and third components in a platelike form. This feature provides the second component (4) with a largesurface area which advantageously facilitates the integration of thesecond component (4) with fibrous tissue growth. As also shown in FIG.4, through holes (6) may be provided in the plate like extension of thesecond component (4), which further increase the external surface areaand also allowing tissue to grow through the second component furtherfacilitating integration. Although the above description refers to aseries of components, it will be appreciated that each component may bea portion of an integral element manufactured from a single piece ofmaterial. It is, however, preferred that a frangible linkage is providedbetween the third and second components or between the second and firstcomponent, so that in the event that a high load is applied to the thirdcomponent, or to a member attached thereto, the linkage will fair so asto protect the implanted bone from injury.

While the present invention has been described with particular referenceto the provision of a prosthesis for replacement of lost digits orlimbs, the invention is also applicable to other prosthesis which extendthrough the skin, e.g. dental implants.

Although only preferred embodiments are specifically illustrated anddescribed herein, it will be appreciated that many modifications andvariations of the present invention are possible in light of the aboveteachings and within the purview of the appended claims withoutdeparting from the spirit and intended scope of the invention.

The invention claimed is:
 1. A transcutaneous prosthesis whichcomprises: a first component adapted for attachment to a bone; a secondcomponent intended for location between the bone and the skin, thesecond component having an outer surface, at least part of which issurface treated for stimulation of fibroblastic cell proliferation andattachment of epithelial cells; and a third component intended forlocation exterior to the skin surface and which extends from the skin inuse, the third component having an outer surface, wherein the outersurface of the third component comprises a low surface energy surface,the low surface energy outer surface being on a portion which isexterior to the skin surface in use and which thereby deters bacterialadhesion; the second component being located between the first componentand the third component in use, such that the low surface energy outersurface of the third component is adjacent to the surface treated outersurface of the second component.
 2. A prosthesis according to claim 1,wherein the components are integrally formed and have different surfacetreatments.
 3. A prosthesis according to claim 1, wherein the firstcomponent has a surface treatment which stimulates bone growth andosseous integration.
 4. A prosthesis according to claim 1, wherein thesecond component has a micro-pitted surface.
 5. A prosthesis accordingto claim 1, wherein the surface of the second component carries afibronectin or laminin coating.
 6. A prosthesis according to claim 1,wherein the second component extends outwardly from the first and thirdcomponents.
 7. A prosthesis according to claim 6, wherein the secondcomponent has through holes.
 8. A prosthesis according to claim 1 wherethe third component carries a coating comprising a fluoro- or siliconepolymer.
 9. A prosthesis according to claim 1, wherein the thirdcomponent carries a coating comprising diamond like carbon.
 10. Aprosthesis according to claim 1, wherein the third component includes afrangible or detachable linkage which permits an external component todetach in the event that an unusually high load is applied to theprosthesis.
 11. A prosthesis according to claim 1, in which the thirdcomponent is connected to an artificial limb or digit.
 12. A prosthesisaccording to claim 1, wherein the surface of the second componentcarries a protein coating.
 13. A prosthesis according to claim 1,wherein the surface of the second component carries a hydrated calciumphosphate coating.
 14. A prosthesis according to claim 13, wherein thehydrated calcium phosphate coating is a coating of hydroxy apatite. 15.A prosthesis according to claim 1, wherein the outer surface of thethird component comprises a non-stick material.
 16. A prosthesisaccording to claim 1, wherein the surface energy of the third componentis a surface energy level of a non-stick material comprising a fluoro orsilicone polymer or diamond-like carbon.
 17. A prosthesis according toclaim 1, wherein the first component is shaped for implantation into abone.
 18. A prosthesis according to claim 1, wherein the secondcomponent extends outwardly with reference to the first and thirdcomponents in a manner that increases an external surface area of thesecond component.
 19. A prosthesis according to claim 1, wherein thesecond component is mushroom shaped, thereby increasing a surface areaover which soft tissue can attach.